A liquid crystal panel has been required to be thinner, lighter, more durable, and to consume less power. The liquid crystal panel having these characteristics are utilized not only in mobile devices such as a cellular phone but also in display sections of a personal computer, a home television, and the like. With popularization of the liquid crystal panel, various techniques in packaging have been developed and applied. For example, as a packaging technique of a liquid crystal driver IC which has been developed recently, there has been used a packaging technique utilizing a flexible wiring substrate of a TCP, a COF, and the like, thereby realizing high-density package and a thinner and lighter liquid crystal panel.
The flexible wiring substrate is constituted of (i) a tape base material made of polyimide or the like and (ii) a conductive wiring formed thereon. The conductive wiring is formed by photo-etching with Cu or the like. It is often that installation parts and the like are soldered on an outermost surface of the conductive wiring. Further, when Cu is used to form the conductive wiring, it is often that the surface of the conductive wiring is coated by Sn, Au, and the like. Further, on the flexible wiring substrate's surface having the conductive wiring, a solder resist is formed on an area other than portions connected to external circuits so as to protect the conductive wiring.
Meanwhile, it is general that the flexible substrate is formed in a long tape manner in manufacturing steps of the TCP and COF in which semiconductor chips are installed. Thus, it is possible to sequentially transport the flexible wiring substrate to production apparatuses used in the respective manufacturing steps, so that it is possible to efficiently form a module on an assembly line. Further, the flexible wiring substrate is formed in a tape manner, so that it is possible to supply and collect the flexible wiring substrate by rolling it up with a reel. Thus, the flexible wiring substrate formed in a long tape manner is advantageous in mass-production of semiconductor devices.
As described above, as to the flexible wiring substrate, a module is formed by installing semiconductor chips and other parts. In this case, connectors may be formed on the flexible wiring substrate as connection terminals, which allow connection with external circuits, for the sake of convenience in assembling and replacing installation parts. Thus, in the periphery of the connectors of the flexible wiring substrate, reinforcement is required so that the flexible wiring substrate is not damaged by a mechanical load exerted in connecting the external circuits to the connectors. Accordingly, it is necessary to enhance the strength of the flexible wiring substrate by combining a reinforcement with a surface positioned on a back side of a connector-installation area of the flexible wiring substrate.
The following description explains examples of a conventional reinforcement combining apparatus and a method of combining the reinforcement with the flexible wiring substrate with reference to FIG. 7 to FIG. 9.
FIG. 7 is a cross sectional view schematically showing an important portion of a reinforcement combining apparatus for combining a reinforcement with the flexible wiring substrate. As shown in FIG. 7, a pressing surface 102 of a stage (lower holding member) 101 and a pressing surface 104 of a tool (upper holding member) 103 are positioned opposite to each other in parallel. Between them, a flexible wiring substrate 105 formed in a long tape manner is disposed so that its surface having conductive wiring (not shown) faces upward. The flexible wiring substrate 105 is disposed at the foregoing position by means of a sprocket and a transport reel (that are not shown). Then, a reinforcement 106 is disposed on the pressing surface 102 of the stage 101.
The reinforcement 106 is made of polyimide, PET, and the like, and adhesive 107 used to bond the reinforcement 106 to the flexible wiring substrate 105 is applied to a bonded surface of the flexible wiring substrate 105 in advance.
FIG. 8 shows a condition under which the reinforcement 106 is combined with the flexible wiring substrate 105 by using the reinforcement combining apparatus of FIG. 7. As shown in FIG. 8, a position of the reinforcement 106 disposed on the stage 101 and a position of the flexible wiring substrate 105 are adjusted, and the stage 101 is raised, and the tool 103 is made to descend. The stage 101 and the tool 103 press the flexible wiring substrate 105 and the reinforcement 106 so that they are combined with each other.
Here, the adhesive for bonding the flexible wiring substrate to the reinforcement is described. As the adhesive, it is possible to use a normal temperature type having an adhesive force at normal temperature and a thermosetting type having an adhesive force when heated. In case of using the normal temperature type, when a bonding condition is set so that: bonding temperature is normal temperature, and a bonding time is 0.5 seconds, and a bonding pressure is 0.5 Kg/cm2, it is possible to preferably bond the flexible wiring substrate and the reinforcement to each other.
However, in case of bonding the normal temperature type adhesive, when a heating process such as solder reflow is performed after bonding the reinforcement, the adhesive which comes out due to the heating is sometime transcribed to an unnecessary portion or spattered, so that this deteriorates the quality of the semiconductor device. Further, the normal temperature type adhesive has an adhesive force after the bonding, so that this raises such problem that: when an external shape of the flexible wiring substrate is punched out, the adhesive adheres to a punching die.
Meanwhile, in case of adopting the thermosetting type as the adhesive, when a bonding condition is set so that: bonding temperature (of both the tool 101 and the stage 103) is 200° C., and a bonding time is 3 seconds, and a bonding pressure is 28 Kg/cm2, it is possible to preferably bond the flexible wiring substrate and the reinforcement to each other. In steps performed thereafter, the adhesive completely sets, so that it is possible to avoid the foregoing troubles brought about by using the normal temperature adhesive.
In this manner, the thermosetting type adhesive is used as the foregoing adhesive, so that troubles caused by the adhesive can be solved. However, the following problems are brought about in pressing the flexible wiring substrate and the reinforcement so that they are combined with each other.
FIG. 9 shows an enlarged view of a connection portion between the flexible wiring substrate and the reinforcement that are pressed by the reinforcement combining apparatus shown in FIG. 8. As shown in FIG. 9, a solder resist 1011 is an outermost layer of the flexible wiring substrate, so that mainly the solder resist is in contact with the pressing surface 104 of the tool 103 with it pressed by the pressing surface 104. Thus, the adhesive 107 corresponding to an area having the solder resist 1011 receives pressure, but the adhesive 107 corresponding to an area having no solder resist 1011 receives less pressure.
Here, the adhesive 107 has an adhesive force. Thus, even when the adhesive 107 does not completely receive the pressure, it is possible to bond the reinforcement 106 and the flexible wiring substrate 105 to each other. However, air bubbles may occur in (i) an interface between the adhesive 107 and the reinforcement 106 or the flexible wiring substrate or (ii) the adhesive 107, so that the air bubbles may deteriorate the bonding property. That is, in order to remove the air bubbles, it is necessary to press the adhesive 107 to some extend.
Thus, when the adhesive 107 has a portion which receives less pressure, there occurs a portion which is not sufficiently bonded, so that this raises such problem that the reinforcement 106 exfoliates from the flexible wiring substrate 105.
Further, in the flexible wiring substrate to which the reinforcement has been bonded, in case of installing the connectors positioned on the backside of the surface bonded to the reinforcement, the connectors are subjected to reflow process by using solder and the like, thereby installing the connectors. Here, in case where the air bubbles occur in the adhesive 107, when the flexible wiring substrate is put into a reflow oven, the air bubbles swell due to the drastic rise of temperature, so that this deteriorates the bonding property.
Further, when the air bubbles swell in the adhesive 107, this brings bout not only the deterioration of the bonding property but also the following problem. For example, in a flexible wiring substrate used as a driver of a liquid crystal display, a large number of terminals for receiving a signal such as a voltage, timing, data, bias for operating a semiconductor device, are installed. Thus, it is required to provide a larger number of connector pins on the flexible wiring substrate so as to cover the large number of terminals. Accordingly, it is necessary to make a pitch of the pins for surface mounting finer. Further, it is required to set the flatness in a connection surface of each connector to be within an error range of approximately dozens μm so as to realize preferable connection. However, when the air bubbles occur in the adhesive 107, the flatness of the connector is deteriorated, so that the connection property between the connectors and the external circuits is deteriorated. As a result, so-called connection failure occurs.
Meanwhile, as a method of combining the reinforcement with the flexible wiring substrate, Japanese Unexamined Patent Publication No. 170031/1995 (Tokukaihei 7-170031)(Publication date: Jul. 4, 1995) proposes a method in which: (i) a reinforcement having holes for positioning, (ii) a flexible wiring substrate having holes for positioning, and (iii) a buffer material having escape holes are sequentially put into a positioning pin which is provided on a drag, and these members are pressed by a top force, thereby combining them with each other. However, this method requires a combining operation for each process, so that it is impossible to freely provide a combination of the flexible wiring substrate and the reinforcement. Thus, the foregoing method does not cover sequential processes for combining the reinforcement with the flexible wiring substrate in manufacturing a TCP and a COF by means of a general reel-to-reel process which allows the reinforcement and the flexible wiring substrate to be freely combined. Thus, the method is not suitable for mass-production.